The effect of urea on alpha-helical structure of requiem shark myosin

Myosin and its fragments, rod and subfragment-1 (S1), were prepared from th e requiem shark Triakis scyllia and examined for the effects of urea on the ir alpha -helical structure by monitoring with circular dichroism (CD) usin g corresponding proteins prepared from the carp Cyprinus carpio as referenc es. All of the protein preparations from requiem shark showed decreased alp ha -helical contents with increasing urea concentrations. However, rod was most stable against urea treatment, whereas myosin and S1 exhibited similar patterns in urea concentration-dependent decrease of alpha -helix. When co mpared with the above results for requiem shark, proteins prepared from car p were less stable in terms of alpha -helical structure at least up to 2 M urea examined in the present study, irrespective of myosin and its fragment s. Furthermore, alpha -helical structure of myosin, rod and S1 from requiem shark were completely refolded when urea was removed from the sample solut ions. On the other hand, the refolding of alpha -helix in carp proteins aft er urea treatment was not perfectly accomplished, especially in the case of myosin and S1. Taken together, it is concluded that the alpha -helical str ucture of requiem shark myosin is highly resistant to urea denaturation.